Cores from the Deep Sea Drilling Project contain evidence that liquid hydrocarbons are migrating in or into near-bottom sediments at three widely separate locations. The first occurrence noted was the highly publicized, visually observed accumulation of immature petroleum in sediments on the Challenger Knoll in the Gulf of Mexico. Later, systematic chemical analyses revealed two more possible examples of migrated hydrocarbons. The first of these was a low-grade bitumen enrichment in a thin porous zone in Pleistocene sediments on the Shatsky Rise in the western Pacific Ocean. The second was a small but geochemically significant quantity of gasoline-range hydrocarbon and wet gas that apparently has seeped upward into Miocene sediments in the Balearic basin of the western Me iterranean Sea. These migrated hydrocarbons, in addition to the methane gas frequently found in the deep-ocean cores, reveal that hydrocarbon source rocks must be present, at least locally, in deep-ocean sediments, because liquid as well as gaseous hydrocarbons have begun to migrate.